An endodontic hand file used in clinical endodontic practice typically is a stainless steel or nickel titanium file attached to a plastic handle with a moveable rubber stopper. The rubber stopper is used for measuring the length of a root canal by aligning it with a reproducible landmark on the tooth. The rubber stopper is pierced through the metal portion of the file. Once the file is placed in a canal and moved to the very end/tip/apex of the root canal, the rubber stopper is moved to a tooth reference point which can then be measured on a small hand rule. Length verification can be done with a radiograph (x-ray). With the advent of an electronic apex locator, a clip is attached to the metal portion of the file and the clip is connected by a wire to the electronic apex locator which provides a read out as the file is moved toward the apex of the root canal. A second patient “lip” click is also used to complete a circuit. Once the device registers the proper length, the rubber stopper is adjusted to the tooth reference point. The clip is then removed and the entire file is withdrawn from canal length and measured on a small hand ruler, thus establishing the working length for that particular canal.
While the endodontic instruments currently known, in which an endodontic file is used in conjunction with an electronic apex locator, are helpful in determining a tooth root canal length, they have several limitations.